The present invention relates to a new and improved construction of gear measuring feeler.
In its more particular aspects, the present invention relates specifically to a new and improved construction of gear measuring feeler including a feeler rod which is pivotably mounted in a housing. This feeler rod supports a feeler probe at one of its ends and, at the other one of its ends, one of two relatively movable members of a measuring system. The measuring system generates a magnetic field and delivers electrical signals which are proportional to the deflection of the feeler probe, to a matching circuit standardizing the electrical signals. The two relatively movable members of the measuring system comprise means for generating a static magnetic field and a Hall-effect sensor, respectively, and the matching circuit is mounted at the housing.
In such a gear measuring feeler, as disclosed in the aforementioned commonly assigned, copending U.S. application Ser. No. 06/560,999, now U.S. Pat. No. 4,528,758 the matching circuit or electronic component 56 which is connected to the output of the Hall-effect sensor 50 essentially comprises a zero compensation circuit 74 and two series-connected operational amplifiers 76 and 78. The zero compensation accomplished by means of the zero compensation circuit 74 is required in such gear measuring feeler because the Hall-effect sensor 50 is only operated at one d.c.-voltage level, whereas during measurements at tooth flanks with such gear measuring feeler a deflection of the feeler probe must be measured from a pre-adjusted zero position in the plus-direction or minus-direction. Since, on the one hand, only a unidirectional voltage is present in the form of the d.c.-voltage and since, on the other hand, the measured voltage at the output should be as informative as possible, i.e. a deflection, for instance, to the left should generate a positive voltage and a deflection to the right a negative voltage, the output voltage of the Hall-effect sensor 50 must be symmetrized. For this purpose the zero compensation circuit 74 supplies a voltage which is added to the output voltage of the Hall-effect sensor 50 before this output voltage is fed to the operational amplifier 76. The zero compensation circuit 74 contains a reference voltage transmitter 80 which supplies a thermally stable voltage independently of eventual fluctuations of its current supply source. Furthermore, the zero compensation circuit contains a potentiometer P2 at which the zero compensation voltage can be adjusted such that no mechanical fine adjustment or tuning of the measuring system is required.
Uncertainties with respect to the measuring result can occur in the gear measuring feeler according to the initially cross-referenced commonly assigned, copending U.S. patent application if the zero compensation circuit 74 and the remaining parts of the measuring circuit do not have exactly the same temperature drift. Common mode or in-phase voltages can result from the Hall-effect sensor which must be suppressed by special additional measures. It has furthermore been found that the measuring result could be further improved if it were possible to increase the output voltage of the Hall-effect sensor, i.e. its sensitivity in terms of millivolt per micrometer feeler probe deflection.